Longwall supports are disclosed, for example, in DE 42 02 246 A1. A longwall support of this type consists of a coal cutting machine or plow, which is driven by a cable, a conveyor, and longwall support units. The conveyor extends in front of the working face and includes a channel, in which an armored conveyor moves along the working face. The channel is divided into individual units. While these units are interconnected, they are able to perform a movement relative to one another in the working direction. Each of these units connects by means of a cylinder-piston unit (advance cylinder) to a longwall support unit. Each longwall support unit serves the purpose of propping the mined longwall. Each longwall support unit is mounted on runners and comprises a roof construction, which is stayed relative to the runners by cylinder-piston units, and serves to support a hanging roof.
In addition, stays are provided, which exert on the conveyor a force that is inclined in the conveying direction. These stays are typically cylinder-piston units, which are each supported on the one hand on a longwall support unit and on the other hand on the channel unit that faces an adjacent longwall support unit. As a result, these stays exert one force component that is directed against the working face, which is called advance force in the present application, and another force component in the conveying direction, which is called staying force in the present application.
The use of the stays permits compensating longitudinal forces that act upon the channel/conveyor. These are not only forces that result from the conveyance, but also weight forces, which result from the fact that the working face and, with that, also the conveying plane are inclined over the entire length of the longwall or also only over a part of the length. To compensate the forces, one may provide, for example, every third, fourth, tenth longwall support unit with such a stay, which is preferably stayed in facing relationship with the next, directly adjoining longwall support unit.
The number of the stays and the pressure adjusted therein are typically determined by computation or estimation of the extent of the forces which are to be expected and to be compensated in the longitudinal direction of the conveyor.
It is therefore an object of the invention to minimize the stays with respect to their number and with respect to the pressure that is to be adjusted in them, to keep expenditure of the systems low with respect to investment and operation, and to integrate the stays into the longwall face operation such that the stays assume an important function in the mining and conveying of rock and/or coal.